Although it will be apparent that its usefulness is not limited thereto, the invention has particular applicability to steam systems wherein it is desirable to separate condensed vapor and other materials from the working vapor.
During warmup in a steam supply system, large amounts of condensate, air and other gases are invariably found in the system and should be separated from the working vapor quickly for operational efficiency. Even after warm-up, some of the undesirable products are produced. Condensate formation is in large part due to pipe heat losses which result from heat radiation, convection and conduction through the pipe walls and occurs whether or not the pipes are insulated. Condensate is also formed due to the performance of work in the various applications of the system and is found in the dead-end sections of piping. No matter how formed, it causes a number of undesirable effects such as reduced system capacity for steam flow, water hammer, erosion due to the friction of fluid flow, corrosion due to dissolved oxygen and the presence of carbonic acid and damage to machinery due to high moisture content of the steam. In addition, the condensate, air, CO.sub.2 and non-condensable vapors, reduce the heat transfer and have other undesirable side effects. In addition, dirt, rust and scale invariably accumulate, particularly when the system has been shut down for any appreciable period of time. As is recognized by those skilled in the art, it is fundamental that for efficient operation, all of these components should be removed from the system with a minimum loss of vapor and with the condensate preferably being returned to the feed tank for redelivery to the steam generating equipment.
According to conventional practice, steam traps of various classes are used in drain lines at points throughout the steam system where condensate may be found so as to remove the condensate and other materials as described above. One class of steam trap commonly employed is the thermostatic trap. These usually have a bellows or a bi-metallic element which fully or partially opens a valve to allow the passage of the condensate and undesirable gases when the temperature at the thermostatic element is below a predetermined value hereinafter termed the actuating temperature.
During the warmup stage of operation, when the temperature is well below the actuating temperature, the bellows or bimetallically controlled valve is in the open position and will pass the large amounts of condensate and other products present in the drain line. Once the warmup stage is passed, the preselected actuating temperature is reached and the thermostatic element closes the valve until condensate accumulates, at which point a condition of temperature imbalance develops, cooling the thermostatic element and causing the valve to open when the temperature is below the actuating temperature. It should be noted that in a typical installation the thermostatically operated trap cycles between the open and closed position on a regular basis. By way of example, it is not uncommon for such a trap to open and close 75,000 or more times a year. This continuous cycling leads to wear due to the constant operation of the thermostatically operated valve in seating and unseating as well as to fluid friction. This wear rapidly becomes appreciable during prolonged periods of operation. In relatively short periods of time the wear leads to leakage which is in addition to the normal seat leakage caused by mismatching of parts. Thus, cyclic operation soon leads to an appreciable loss of steam and reduction in the efficiency of the system. Even though a trap might be capable of blocking almost all vapor when it is new, it becomes a source of gradually increasing vapor leakage during its life span.
A further problem which is more acute in the case of bellows-type thermostatically operated traps, is that the bellows are subject to fatigue stressing as they are cycled and to damage by pressure surge and water hammer. Eventually failure of the bellows will occur if the traps are not replaced on a regular basis. When the bellows-type fails it fails in the open position, causing large amounts of steam to escape from the system until the source of the problem is located and corrected.
Although bimetallic type traps are not as subject to pressure surge or water hammer damage, these traps are affected by hysterisis losses with use so that their response characteristics change over a period of time.
The cyclic nature of the operation is also a cause of pressure and temperature fluctuations in the system and is thus a source of system inefficiency. In addition, these fluctuations create turbulence around the valve which contributes to valve wear.
One answer to many of the foregoing problems is the use of continuous drain orifice assembly of the kind shown in U.S. Pat. No. 3,877,895 owned by the assignee of this application and in U.S. Pat. No. 3,715,870. This assembly is a continuous condensate removal device with an orifice sized to pass the condensate produced in the system with a stable but nominally small steam loss. It is an effective and highly efficient condensate removal device when employed in a steam system in locations where the condensate load is predictable and load fluctuations are not a problem.
During warm-up and in certain other operations where condensate load fluctuates over a wide range, a thermostatic steam trap is more effective in that it is capable of automatically passing the large amounts of condensate produced under these conditions. However, for the reasons expressed above, the thermostatic steam trap is not as effective a device as a continuous drain orifice once the system has stabilized.